J.G. de Lint contributed a thorough discussion of the portraits of Leeuwenhoek.

The fourteen letters in the original Dutch transcribed by Leersum are on pages facing an English translation by Dr. A. Querido. These letters were all included in the first two volumes of Alle de Brieven / Collected Letters in fresh translations.

Why was this volume necessary?

Leeuwenhoek's self-published letters began with the letter of April 25, 1679 to Nehemiah Grew, the letter numbered 43 in Alle de Brieven / Collected Letters. According to Leeuwenhoek's own numbering, this was the 28th letter. What happened to the first 27? For that matter, what happened to the first 42?

Seventeen were published in Philosophical Transactions. Fourteen others, however, were not published until 1930 in this volume. That's a total of 31. The other 12 were not published until Alle de Brieven / Collected Letters.

Dobell accounts for the first 27 in his biography beginning on page 356. A few years earlier, he wrote a more complete accounting for Opuscula Selecta Neerlandicorum, which was published in book form with the fourteen previously unpublished letters.